Ammunition sabot



United States Patent Ofi ice 3,164,692 Patented Jan. 1965 3,164,092 AMMUNITIUN SABOT David S. Reed, Stratford, Rex E. Dickey, Huntington, and Roland L. Bescher, .lr., Fairfield, Conn., assignors to Remington Arms Company, ind, Bridgeport, Conn, a corporation of Delaware Filed Nov. 13, 1962, Ser. No. 237,217 4 Claims. ((31. 102-93) This invention relates in general to a new and improved plastic sabot adapted to be attached to small arms ammunition. More particularly, the invention relates to a unitary sabot which is adapted to be released from the projectile quickly and cleanly after leaving the muzzle of the gun so as not to disturb the course of the projectile.

It is well known in the field of ballistics that when a projectile passes through a gun bore at high speed, the friction between the projectile jacket and the barrel generates a considerable amount of heat. This friction causes barrel erosion or wear which results in ineffective gas sealing which results in considerable loss of projectile velocity and erratic flight of the projectile.

In the past, various types of positive gas seals have been provided with projectiles in an effort to (1) provide an eifective gas seal; (2) reduce barrel wear; and (3) increase velocity and accuracy of the projectile. Some of these have included complicated arrangements made of two or more materials with special means to hold the sabot on the projectile.

Other types require elaborate means to remove the sabot from the projectile after leaving the muzzle of the gun. Very often, the detached sabot itself becomes a dangerous projectile which is a source of accidents to nearby persons who happen to be in the line of fire. This is especially troublesome in the military where a shooter very often fires over his own men. In many instances, if the sabot does become disengaged from the projectile, in doing so, the course of flight of the projectile is disturbed and poor accuracy results.

More recently, sabots have been molded directly on to the projectile and a second type of material provided as a shell over the molded material.

It is an object of this invention to provide a unitary sabot made of a thermoplastic resin which is grooved longitudinally to form segments connected by relatively easily fractured web portions.

It is another object of this invention to provide a unitary plastic sabot in which a projectile is secured by an interference fit and which upon leaving the muzzle of a gun fractures into a plurality of elongated strips. These strips remain attached to the sabot but peel back rapidly to form a sabot diameter approximately three times its original diameter, thereby greatly increasing the air drag load on the sabot causing it to decelerate and fall off of the projectile.

It is another object of this invention to provide a sabot which is economical to manufacture and readily assembled on a small arms projectile.

It is another object of this invention to provide a plastic sabot which will act effectively as a gas seal, will substantially increase the velocity of the projectile over a conventional cartridge and which breaks away from the projectile without affecting the flight course of the projectile.

It is yet another object of this invention to provide a sabot which permits the use of a larger amount of powder for a given caliber of projectile, thus increasing the possible maximum velocity of the projectile.

It is yet another object of this invention to provide a plastic sabot which will permit the firing of a projectile in an oversize bore.

Other objects will be apparent from the specification and claims.

FIGURE 1 shows an elevation view'of the sabot attached to a bullet.

FIGURE 2 shows a plan view of the sabot.

FIGURE 3 shows an elevation view of the sabot.

FIGURE 4 shows a View of the sabot in the expanded condition after having become disengaged from' the bullet.

Referring to the drawings, a projectile 19 is shown inserted in a recess 12 of the sabot-14. The recess is tapered slightly inwardly from top to bottom and has a diameter slightly less than the diameter of the projectile so that the projectile can be held securely in the recess 12 by means of an interference fit.

The sabot 14 is preferably a one-piece injection molded plastic member having a relatively high impact strength,

as explained below. The sabot comprises a cylindrical base member 16, the thickness of which depends on the explosive force required to propel a projectile a desired velocity. The base must be of sufficient strength so as not to deform excessively under explosive pressure upon firing of the gun.

Distributed symmetrically around the circumference of the sabot 14 and forming an extension of the base 16 are six wall segments 18, the segments being separated by axially-extending V-shaped grooves 20 of proper'depth' to form a thin plastic membrane 22. The inner portions of the membranes and the inner faces of the wall segments define the recess 12 which receives the bullet or projectile 10.

The sabot is designed to provide alignment and support for the bullet while travelling through the bore of a rifle or pistol, imparting rotation to the bullet through the interference fit which prevents slippage during the time interval that the projectile is subjected to acceleration and Operation The combined sabot-bullet, upon leaving the muzzle at high velocity and at a high rotational speed,"is acted upon by centrifugal force and air pressure loads, which effectively cause separation of the sabot 14 and. bullet 10 withina very short distance (12" to 18") from the muzzle. Air pressure acting against the angular forward surfaces 28 of the six side walls 18 combines with centrifugal force to fracture the thin plastic membranes 22 which join the wall segments 18 together. This results in a rapid radial flaring, or peeling of the segments 18 which remain attached to the sabot base16 and which open out flat to enlarge the sabot to approximately three times its original diameter. The mushroomed sabot great 1y increases the air drag load on the sabot, causing it to decelerate and become disengaged, thus allowing the bullet to continue undisturbed along its trajectory path to the target.

It can be appreciated that a certain velocity of the sabot is required in order to obtain fracturing of the thin plastic membranes 22. However, this necessary fracturing velocity can be varied by changing the fracturing area or the thickness of the membranes 22. i

From the results of testing various types of plastics, it appears that a relatively high impact strength is required in order for the sabot to act in the manner required. Thus, nylon polyamide resin, Delrin, acetal resin, and

If extended, these inclined faces would Cl Teflon fluorocarbon were tried and proved to be un successful when the sabots disintegrated upon leaving the gun muzzle. Sabots made of high density polyethylene disintegrated in the gun barrel.

In order to succeed in this use, a plastic must possess sui'ficient flexibility to permit a good interference fit between the bullet and sabot, must have sufiicient strength to prevent excessive distortion under explosive pressure, and must have suflicient impact strength to withstand the shock of explosive discharge and to permit the wall segments to be peeled back without tearing loose from the sabot base. A plastic which meets all of these requirements is a thermoplastic polycarbonate resin.

Two polycarbonate resins which were tested and which proved successful for the purpose intended were Lexan polycarbonate resin made by the General Electric Company and Merlon polycarbonate resin made by the Mobay Products Company, a subsidiary of Mobay Chemical Company. Lexan is described in the April 1958 issue of Modern Plastics Magazine, published by Breskin Publications, Inc., and on pages 47-50 of the May 1, 1961, issue of Product Engineering. Merlon is described in Technical Information Bulletin No. 41-M1 (January 4, 1960); T18 No. 41-M1A (January 12, 1960); TIB No. 44-M2 (February 12, 1960); all issued by the Mobay Products Company.

Generally, the polycarbonate resins can be defined as:

where R is Lexan is described in the above cited publications as ["CGII4C(CH3)2C6H4 0]n The above publications describe the polycarbonate resins which were found to be acceptable for use as sabots. It can be seen that these products have a listed impact strength of 1216 ft. lbs./in. of notch as measured by the standard A.S.T.M cantilever-beam Izod notch test D256. This test determines the energy absorbed in breaking a notched specimen by a single blow, the results of which are stated in terms of impact value, indicative of the total energy to break a standard specimen by a single blow under standard conditions. Results of the Izod impact test should not be generalized and applied quantitatively to other sizes of test specimens or other conditions, however.

All of the plastics which failed as sabots had published impact strength value less than 12 ft. lbs/in. of notch with indications that the higher impact strength values above 12 were preferred.

What is claimed is:

1. A unitary plastic sabot for projection through a rifled gun barrel, said sabot comprising a cylindrical member having a central recess in one end thereof, thus 6 forming a continuous, ring-type projection, a plurality of V-shaped grooves on the outer periphery of said projection, said grooves being radially spaced and extending axially on said projection to form a plurality of wall segments held together by weakened connecting portions, said sabot being made of a plastic which is flexible enough to permit an interference fit of a projectile in said central recess and of sufficient impact strength to prevent disintegration of said sabot within the bore of the gun upon firing of a cartridge with the sabot and projectile so that upon being explosively projected out of the bore of the gun, the weakened connecting portions rupture to permit the wall segments to peel back like a mushroom, without becoming disconnected from the sabot, thus providing a substantially greater wind-resisting area which cooperates with the wind resistance to strip the sabot cleanly from the projectile.

2. A sabot as recited in claim 1 in which said plastic sabot is a polycarbonate resin thermoplastic.

3. A sabot as recited in claim 1 in which said sabot is made of plastic having an impact strength value of at least 12 ft. lbs/in. of notch as measured by a standard notched Izod test.

4. A projectile having a unitary plastic sabot thereon for projection through a rifled gun barrel, said unitary plastic sabot comprising a cylindrical base, skirt means on the lower end of said base to prevent gas leakage, a plurality of wall segments integral with the top of said base and extending upwardly therefor, means of a material having lower impact strength than said wall segments interconnecting said segments, a central longitudinal recess means formed in said wall segments adapted to secure said projectile therein by an interference fit, said interconnecting means having a sufficiently low impact strength and said wall segments having a suificiently high impact strength so that upon being explosively projected, the sabot engages the rifled bore of the gun in gas-sealing and radially supporting relationship and upon being rotatively projected out of the gun muzzle, said interconnecting means ruptures and the wall segments peel back without tearing away from the lower end of the sabot to form a mushroomtype object having a substantially greater wind-resisting area than the original sabot.

References Cited in the file of this patent UNITED STATES PATENTS 395,897 Hartley Jan. 8, 1889 553,062 Follett Jan. 14, 1896 2,663,259 Catlin et a1 Dec. 22, 1953 2,983,224 Prosen et al May 9, 1961 2,998,779 MacRoberts Sept. 5, 1961 3,099,958 Daubenspeek et al Aug. 6, 1963 FOREIGN PATENTS 1,177,047 France Dec. 1, 1958 1,255,572 France Jan. 30, 1961 OTHER REFERENCES Solid Propellant Rockets, second stage, by Alfred J. Zaehringer, pub. by American Rocket Co., Wyandotte, Michigan, 1958; page 210 required, 

1. A UNITARY PLASTIC SABOT FOR PROJECTION THROUGH A RIFFLED GUN BARREL, SAID SABOT COMPRISING A CYLINDRICAL MEMBER HAVING A CENTRAL RECESS IN ONE END THEREOF, THUS FORMING A CONTINUOUS, RING-TYPE PROJECTION, A PLURALITY OF V-SHAPED GROOVES ON THE OUTER PERIPHERY OF SAID PROJECTION, SAID GROOVES BEING RADIALLY SPACED AND EXTENDING AXIALLY ON SAID PROJECTION TO FORM A PLURALITY OF WALL SEGMENTS HELD TOGETHER BY WEAKENED CONNECTING PORTIONS, SAID SABOT BEING MADE OF A PLASTIC WHICH IS FLEXIBLE ENOUGH TO PERMIT AN INTERFERENCE FIT OF A PROJECTILE IN SAID CENTRAL RECESS AND OF SUFFICIENT IMPACT STRENGTH TO PREVENT DISINTEGRATION OF SAID SABOT WITHIN THE BORE OF THE GUN UPON FIRING OF A CARTRIDGE WITH THE SABOT AND PROJECTILE SO THAT UPON BEING EXPLOSIVELY PROJECTED OUT OF THE BORE OF THE GUN, THE WEAKENED CONNECTING PORTION RUPTURE TO PERMIT THE WALL SEGMENTS TO PEEL BACK LIKE A MUSHROOM, WITHOUT BECOMING DISCONNECTED FROM THE SABOT, THUS PROVIDING A SUBSTANTIALLY GREATER WIND-RESISTING AREA WHICH COOPERATES WITH THE WIND RESISTANCE TO STRIP THE SABOT CLEANLY FROM THE PROJECTILE. 